Republican presidential frontrunner Donald Trump, known for his frequent use of coarse and profane language on the campaign trail, scolded former Mexican President Vicente Fox at Thursday night's GOP debate for using a curse word while saying he would not help pay for Trump's proposed wall across the U.S.-Mexico border.

Trump has made building the wall a key plank of his campaign platform and has insisted that the Mexican government would pay for its construction.

"I’m not going to pay for that f---ing wall!” Fox said earlier Thursday in an interview for Fusion. “[Trump] should pay for it. He’s got the money.”

When debate moderator Wolf Blitzer asked Trump about Fox's comment and how he would persuade Mexico to cover the wall's costs, Trump responded, "I will, and the wall just got 10 feet taller."

"I saw him use the word that he used," Trump continued. "I can only tell you, if I would have used even half of that word, it would have been a national scandal.

"This guy used a filthy, disgusting word on television, and he should be ashamed of himself, and he should apologize."

Florida Sen. Marco Rubio challenged Trump over the real estate billionaire's hardline stance on illegal immigration, saying, "If he builds a wall the way he built Trump Tower he'll be using illegal immigrant labor to do it."

In the Fusion interview, Fox also questioned Trump's allegiance to the Republican Party, or any political party.

"He’s not a Republican. Absolutely not,” Fox said. “Those are not Republican principles. He is not a Democrat. He is just himself. He is egocentric."